Ok, we won't overthink that one, but you're right, there's no such thing. There is only "make relevant for as long as possible".
Even that is limited to a degree because in most cases the hardware will fail and need to be replaced before it becomes obsolete in most cases. Not always to be sure, but when it comes to graphics cards, especially gaming cards, it usually is.
I don't think there is ANY reason to go beyond the 2060 Super for "future proofing" if you plan to stay at 1080p. If however you plan to upgrade to a higher resolution display, 1440p or 4k, then you will ABSOLUTELY want a better card.
I have a 2060 Super and it does ok at 1440p, but in a year or two it will probably start requiring me to drop settings to a degree that I don't want to have to do. Had I planned to upgrade to a 1440p display when I bought that graphics card, I'd have probably opted for a 2070 Super. If you plan to EVER move to a 4k display, then you want the biggest card you can get which of course right now would be either the 2080 Super or TI. Even then, you are not going to see Ultra gaming at 4k on most demanding titles, but it will get you close and it will get you ultra on less demanding titles. I'm sure you probably dont' plan to move to 4k gaming, but it's good to know the facts anyhow so you understand your options and the bigger picture.
2070 Super will likely give you Ultra gaming on the most demanding titles for a while at least, at 1440p. At 1080p, it would give you Ultra gaming on everything, at least from the GPU side of things.